1. Field of the Invention
The present invention relates to a bearing preload structure of a machine tool, which gets a preload force in an axial direction to act on a ball bearing.
2. Description of the Related Art
In a spindle device of a machine tool, a spindle is rotatably supported on a spindle head via a ball bearing. As a conventional structure to fix the ball bearing, Japanese Patent Application Laid-open No. Hei 7-24687, for example, discloses one in which nut members fixed to the axial-direction inside of a spindle and a bearing pressing screwed to a male thread portion on an outer periphery of a tip of the spindle fix ball bearings to fixed positions.
Further, Japanese Patent Application Laid-open No. 2000-237902 discloses one in which nuts shrink fitted and fixed to the inside of a spindle and a stepped portion formed at a tip portion of the spindle fixedly position ball bearings.